function F() {}
F.prototype.a = 2;
function O() {}

O.prototype.a = 1;

O.prototype = new F();
var obj = new O();
console.log(obj.a)

// console.log(obj instanceof O); // false
// console.log(obj instanceof F); // false
// console.log(obj.__proto__ === O.prototype); // false
// console.log(obj.__proto__.__proto__ === F.prototype); // false


var arr = [1,2,3];
var obj = {
  a: 1,
  b: 2,
  c: 3
}
for (const key in obj) {
  console.log(key)
  // if (Object.hasOwnProperty.call(obj, key)) {
    const element = obj[key];
    console.log(element)
  // }
}

for (const iterator of arr) {
  console.log(iterator)
}